1. Field of the Invention
The invention relates to a method and apparatus for separating bio-refuse comprising a biological waste fraction and a plastic waste fraction into its constituent fractions, and to apparatus for carrying out this method.
2. Background Prior Art
A method of the above type is known from EP-PS 11 592. In this reference, an apparatus is used such as is already described in U.S. Pat. No. 2,695,221 for the processing of ores. In both cases, in addition to the sieving, the dust occurring in the sieve drum is also sucked away. In the case of EP-PS 11 952, this is effected in order to free refuse of non-compostable components before it is converted into compost. A hammer mill arranged in the drum also serves this purpose. In a known manner, this hammer mill carries out selective comminution, i.e. elastic components remain essentially uncomminuted, whereas brittle components are subjected to a very intensive comminuting action. In addition, a sieve section is also provided on this known drum for sieving out non-compostable components before the residue is composted.
In more recent times, it has been recognized that a much more effective separation of the refuse components is achieved if the constituent fractions of the refills are collected separately. The above-described known solution (EP-PS 11 592) suffers above all from the fact that far too many foreign components pass into the compost, and it is a known fact as described in the technical literature, that the compost obtained in this way is relatively rich in harmful substances.
However, the concept of separately collecting compostable material, in particular the so-called green waste from the garden and possibly also from the household (the most frequently used generic term is "bio-refuse"), still involves the problem that this refuse also contains various plastic components. The reasons for this are many and consist, on the one hand, in the fact that plastic components are carelessly thrown away and can then enter into the same fraction as the garden waste when the latter is collected with a rake; on the other hand, refuse sacks of plastic are usually used which are torn up by machine, so that the remaining portions of the sacks can also remain in the green refuse fraction. Household bio-refuse is also frequently not separated with sufficient care.
EP-PS 82 815 describes a method by which extensive removal of harmful components is possible from a compostable fraction. In this process--in the same way as in the prior art described above--refuse comprising a mixture of materials is sieved before further processing. This method is excellent for refuse mixtures and can naturally also be used for green waste in order to separate out the foreign components. However, as in all separating processes, a certain residual proportion of foreign materials will always occur in the compost.